1. Field of the Invention
The present invention relates to noise reduction circuits for reducing noise contained in signals.
2. Description of the Related Art
A conventional noise reduction circuit having the following structure has been known (see Non-Patent Document 1).
FIGS. 5A to 5C are views for explaining the basic principle of conventional noise suppression. A plurality of image data sets (e.g., TV signals) shown in FIG. 5A are stored in frame memories shown in FIG. 5B, and an average for the n frames is calculated. For a signal component, if there is no variation among the frames, the original signal component value is output as the average value. For noise, on the other hand, since it is considered that there is no correlation among the frames, the average noise amplitude is attenuated to 1/n0.5 as shown in FIG. 5C.
[Non-Patent Document 1]
“7.3.3 image noise suppressing” in p. 115 in “Digital Signal Processing of Images” by Takahiko Fukinuki published by The Nikkan Kogyo Shimbun Co., Ltd.